[Isolated human gastric mucosa cells--studies on physiologic and pharmacologic regulatory mechanisms]

Cells were isolated by use of collagenase, EDTA and pronase form human gastric mucosa obtained at peptic ulcer surgery (n = 61) or at Whipple's operations (n = 6). Enriched parietal cell fractions were prepared by isopycnic centrifugation with Percoll. H+ production, intracellular instrinsic factor and histamine content were maximal in the low density fraction containing 75% parietal cells and--among other nonparietal cell types--mast cells. H+ production, intrinsic factor secretion and adenylate cyclase-activity responded to histamine stimulation in a concentration dependent manner. Response was blocked by histamine H2 receptor antagonists (rantidine, famotidine). Dibutyryl cAMP and the phosphodiesterase inhibitor IMX were the most powerful stimuli whereas carbachol, hexoprenaline and pentagastrin were less effective. Prostaglandin E2 and 6-keto-PGF2 alpha occurred in the highest concentrations in the low density cell fraction. PG production increased linearly for 15 min and seemed to be influenced by the intracellular calcium level.

Effect of famotidine on oxidative drug metabolism

Famotidine, a new H2-receptor antagonist was tested for drug interactions using 14C-aminopyrine and antipyrine. Elimination of these model drugs was studied before and during 8 days of famotidine dosing in 8 healthy volunteers. Famotidine 40 mg b.d. did not inhibit aminopyrine 14CO2 half-life or antipyrine clearance although an unexpected mild enzyme inducing effect could not be excluded. It is unlikely that famotidine will inhibit hepatic drug metabolism during routine clinical use as the daily dose is expected to be 40 mg/day but interactions should be looked for if more prolonged or larger doses are used.

Effects of histamine and related compounds on thyrotropin secretion in rats

The effects of histamine (HA) and related compounds on thyrotropin-releasing hormone (TRH) and thyrotropin (TSH) secretion in rats were studied. Histidine (1.0 g/kg), HA (5.0 mg/kg) or histamine antagonists mepyramine (MP) (100 mg/kg) or famotidine (FA) (5.0 mg/kg) were injected intraperitoneally, and the rats were decapitated at various intervals after the injection. The hypothalamic immunoreactive TRH (ir-TRH) content increased significantly after histidine or HA injection, decreased significantly after FA injection, but was not changed by MP. The plasma ir-TRH concentration did not change significantly after injection of these drugs. The plasma TSH levels decreased significantly in a dose-related manner after histidine or HA injection and increased significantly in a dose-related manner after FA injection. The plasma thyroid hormone levels showed no changes. In the FA-pretreated group, the inhibitory effect of histidine or HA on TSH levels was prevented, but not in the MP-pretreated group. The plasma ir-TRH and TSH responses to cold were inhibited by histidine or HA and enhanced by FA. The plasma TSH response to TRH was inhibited by histidine or HA and enhanced by FA. The inactivation of TRH immunoreactivity by hypothalamus or plasma in vitro after histidine, HA, MP or FA was not different from that of the control. These findings suggest that histamine may act both on the hypothalamus and the pituitary to inhibit TRH and TSH release, and that its effects may be mediated via H2-receptor.

Interaction of ranitidine and famotidine with guinea pig-isolated parietal cells

The inhibitory effects of the histamine H2-receptor antagonists, ranitidine and famotidine on histamine-stimulated gastric acid secretion have been studied in guinea pig isolated, enriched parietal cells using the 14C-aminopyrine accumulation technique. The 14C-aminopyrine accumulation curves in response to histamine were shifted towards the right in a parallel fashion by ranitidine, and in a nonparallel fashion by famotidine. The inhibitory effect of ranitidine, but not that of famotidine, was readily reversed by washing the parietal cells. It is concluded that the histamine H2-receptors in guinea pig parietal cells are blocked competitively and reversibly by ranitidine, but noncompetitively and partially reversibly by famotidine.

Effects of 800 mg cimetidine once daily on gastric acid secretion

Today, the reduction of nocturnal acid secretion is believed to be the most important point in duodenal ulcer therapy. This is supported by the fact that during the day gastric acid secretion is largely buffered by meals. Moreover, independently of food intake the intragastric H+ activity during the day is lower than during the night. During nighttime (2300-0700 h) there was a mean hourly H+ activity of 38 mmol/l--that is, a 65% increase compared with daytime H+ activity with meals--and still a 30% increase without meals. Nocturnal acidity can be suppressed best by single large bedtime doses of H2-receptor antagonists. Cimetidine, 800 mg at night, reduces nocturnal intragastric acidity by 85%; 300 mg ranitidine at night and 40 mg famotidine at night reduce it by 95%. The first clinical trials show that a single nighttime dose of cimetidine or ranitidine is at least as effective in promoting ulcer healing as is twice daily administration.

[Famotidine versus placebo in prevention of the recurrence of duodenal ulcer disease. A multicenter study in Germany, Austria and Italy]

The aim of this study was to gain experience concerning efficacy and safety of famotidine, the new H2-receptor antagonist, for the maintenance of duodenal ulcer disease. 344 patients whose acute duodenal ulceration had recently been healed under famotidine or ranitidine were recruited for a year maintenance treatment with 20 mg bedtime dose of famotidine or placebo. 167 patients were treated with famotidine over 6 and 52 over 12 months. The corresponding numbers in the placebo control were 177 and 21. A life table method of analyses showed that the ulcer relapse rate was consistently and significantly (p less than 0.01) lower on famotidine than on placebo after 6 months (26% [43/167] versus 55% [98/177]). Of the 52 patients treated with 20 mg famotidine at night for further 6 months 7 (14%) developed an ulcer relapse. Of the 21 patients treated for further 6 months with placebo 5 (24%) showed an acute ulcer crater at endoscopy. Famotidine was well tolerated in the longterm therapy. The results confirm the efficacy and safety of famotidine in the prevention of duodenal ulcer relapse for at least 6 months.

MK-208, a novel histamine H2-receptor inhibitor with prolonged antisecretory effect

MK-208 is a guanidinothiazole derivative reported to be a potent H2 blocker devoid of antiandrogenic activity. Its potency and duration of action, in inhibiting pentagastrin-stimulated gastric secretion in man, was evaluated in this double-blind, five-way cross-over trial. Ten healthy male volunteers received single oral doses of placebo, cimetidine 300 mg, and MK-208 5, 10, and 20 mg. A continuous intravenous infusion of pentagastrin (1 microgram/kg/hr) was given 2-4 and 5-7 hr after each oral dose. Gastric contents were continuously aspirated and volumes and acid content determined every 30 min. Plasma levels for MK-208 and cimetidine were monitored over the 7 hr of the study. Cimetidine and all doses of MK-208 significantly inhibited gastric acid secretion in the initial 2-4 hr; however, 10- and 20-mg doses of MK-208 were significantly more potent than cimetidine. In the 5- to 7-hr period, cimetidine 300 mg was not different from placebo, while MK-208 in all doses studied continued to significantly suppress gastric secretion. Plasma levels for MK-208 showed dose-related increments. The results suggest that: (1) MK-208 is a potent inhibitor of gastric secretion in man, in a dose-related fashion at the doses tested; (2) under the study conditions, 5 mg MK-208 was equipotent to 300 mg cimetidine but with greater duration of action, extending at least 7 hr; and (3) these data suggest a future role for this new agent in therapy for acid-peptic disease in man.

Effects of hormones (calcitonin, GIP) and pharmacological antagonists (ranitidine and famotidine) on isolated rat parietal cells

The rationale for the present study was to compare calcitonin and gastric inhibitory polypeptide (GIP) versus two histamine H2 receptor antagonists with respect to their potency of inhibiting parietal cell functions. Adenylate cyclase activity and acid production ([14C]aminopyrine uptake) of isolated rat parietal cells were stimulated by histamine. At 10(-7) and 10(-6) mol/l, calcitonin and GIP reduced the response to histamine by 10-20% following noncompetitive kinetics. Ranitidine and famotidine (MK 208) inhibited the response to histamine by about 50% at 10(-7)-10(-6) mol/l, and at 10(-5) mol/l abolished the histamine effect. On a molar basis famotidine turned out to be 6 times more potent than ranitidine. Both antagonists revealed competitive kinetics. Our data suggest direct inhibition of the parietal cells by the tested compounds which were shown to interfere at the adenylate cyclase cAMP system or at the histamine H2 receptor. However, compared to the histamine H2 receptor antagonists, hormonal inhibition is less pronounced and mediated by a different mechanism.

[I.v. famotidine versus i.v. ranitidine: intragastric pH behavior in surgical intensive care patients]

20 patients of a surgical intensive care unit were treated in a randomised double-blind fashion with i.v. famotidine 10 mg and i.v. ranitidine every 6-12 hours for maximally seven days. Both groups were comparable with respect to the grade of risk of stress-induced bleeding. With both H2-blockers (ranitidine and famotidine) the intragastric pH could be increased to 5.0 and more and kept constant at this level over the whole test period. The mean daily doses required were 22.3 mg for famotidine and 154.3 mg for ranitidine. Stress-induced bleeding as well as adverse reactions could not be observed in both treatment groups.

[Accelerated healing of ulcus ventriculi by a single evening dose of famotidine. Results of an Austrian-German-Italian multicenter study]

An 8 week, double-blind randomized, placebo-controlled multicenter trial was conducted in Austria, Germany and Italy to determine whether famotidine would speed healing and relief of symptoms in patients with benign gastric ulcer. Of the 131 patients who completed the trial, 66 received 40 mg famotidine in the evening and 65 placebo. At 4, 6, and 8 weeks after entry, ulcers had healed in a higher percentage of patients treated with famotidine than of those treated with placebo (47%, 70%, 91% vs 32%, 49%, 61%). In the famotidine group healing had occurred significantly more often after 6 and 8 weeks (p less than 0.05 and p less than 0.01 respectively). Famotidine was superior to placebo in relieving ulcer symptoms. The proportion of patients receiving additional antacid therapy was significantly lower in the famotidine group. The findings suggest that the new H2-receptor antagonist famotidine significantly speeds the healing of benign gastric ulcers in a single evening dose.

Effects of H2-receptor antagonists upon physiological acid secretory states in animals

The results reported in this paper indicate that representative H2-receptor antagonists are capable of maximally inhibiting gastric acid secretion in animals under the two general circumstances in which it occurs physiologically. Interdigestive or basal secretion was examined in chronic gastric fistula rats and food-stimulated secretion in vagally innervated, lesser curvature pouch dogs. The H2 antagonists studied and omeprazole, an inhibitor of the proton pump H+, K+-adenosine triphosphatase, also decreased pepsin secretion in rats, although not to the same maximal degree as acid secretion. Gastric emptying was increased by each H2 antagonist but only at high acid inhibitory doses. Omeprazole, in contrast, did not alter gastric emptying at a similar antisecretory dosage level. In dogs, a representative H2-receptor antagonist markedly inhibited food-stimulated acid secretion. These data suggest that the predominant effect of omeprazole and H2-receptor antagonists upon gastric function is to inhibit acid secretion and that H2-receptor antagonists may be capable of maximally inhibiting endogenous acid secretion in humans, as does omeprazole, if given under proper conditions.

Famotidine, a new, potent, long-acting histamine H2-receptor antagonist: comparison with cimetidine and ranitidine in the treatment of Zollinger-Ellison syndrome

Famotidine, a new, potent, long-acting histamine H2-receptor antagonist was compared with cimetidine and ranitidine in 9 patients with Zollinger-Ellison syndrome. The mean minimum daily requirement of famotidine to control gastric acid hypersecretion was 0.24 g (range 0.08-0.48 g) compared with 2.1 g (range 0.6-3.6 g) for ranitidine and 7.8 g (range 1.2-13.2 g) for cimetidine. Equally potent doses of the three drugs had similar onsets of action, but the duration of action of famotidine was 30% longer than the duration of action of either ranitidine or cimetidine (p less than 0.05). Eight patients were treated for up to 9 mo (mean 6 mo) with good control of gastric acid hypersecretion and with no evidence of biochemical or hematologic toxicity. These studies demonstrate that famotidine is nine times more potent than ranitidine and 32 times more potent than cimetidine, has a longer duration of action than ranitidine or cimetidine, and is both safe and effective in the long-term therapy of Zollinger-Ellison syndrome.

Famotidine, a new H2-receptor antagonist. Effect on parietal, nonparietal, and pepsin secretion in man

We studied pentagastrin-stimulated acid and pepsin secretion with three doses (5, 10, and 20 mg) of a new H2-receptor antagonist (famotidine) administered orally to normal male volunteers. A dose response was identified: 2 hr after oral dosing, 5 mg famotidine suppressed stimulated acid secretion to 60% of control and was comparable to 300 mg cimetidine (55% suppression). Higher doses of famotidine yielded significantly more suppression of acid secretion (10 mg yielding 70% and 20 mg, 90%). Pentagastrin-stimulated acid secretion remained decreased (50% of control) 12 hr after oral dosing with 20 mg famotidine. The reduction in pepsin output paralleled the reduction in acid secretion and was primarily due to a reduction in the volume of secretion and not to a change in pepsin concentration. We calculated the components of gastric secretion (acid from parietal cells) and bicarbonate secretion (from nonparietal cells) and found that the primary effect of the H2-receptor antagonists was a dramatic reduction in parietal cell output without a significant decrease in nonparietal secretion. Famotidine proved to be a potent inhibitor of both the parietal component of gastric acid and pepsin output. Famotidine was significantly more potent than cimetidine; 5 mg of famotidine was comparable to 300 mg of cimetidine.

Cimetidine versus famotidine: the effect on the pharmacokinetics of theophylline in rats

The effects of cimetidine and a new, potent H2-antagonist, famotidine, on the single dose pharmacokinetics of theophylline were examined in rats. Male Sprague-Dawley rats (6 rats/group) received an i.v. dose of theophylline (6 mg/kg) alone and in conjunction with an i.v. dose of famotidine (10 mg/kg) or cimetidine (10 mg/kg). Venous blood samples were collected serially for seven hours after theophylline infusion and analyzed for theophylline concentration by HPLC. Concomitant famotidine administration did not alter any of the pharmacokinetic parameters of theophylline (AUC0- infinity; 38.1 +/- 8.7 vs. 38.8 +/- 6.3 micrograms.hr.ml-1), while cimetidine demonstrated a significant reduction in theophylline systemic clearance (0.11 +/- 0.02 vs. 0.16 +/- 0.02 L/hr/kg; p less than 0.001), a 40% prolongation of half-life (2.8 +/- 0.9 vs. 2.0 +/- 0.5 hr), with no change in the volume of distribution (0.39 +/- 0.1 vs. 0.41 +/- 0.13 L/kg). These results suggest that in contrast to cimetidine, famotidine, a non-imidazole H2-receptor antagonist, does not interfere with theophylline disposition in the rat.

[Famotidine versus ranitidine in the acute treatment of duodenal ulcer. A multicenter comparative study in Germany]

185 patients with endoscopically proven duodenal ulcers were randomly allocated to treatment with either famotidine 40 mg nocte, 20 mg bid, 40 mg bid or ranitidine 150 mg bid for 2-8 weeks in a prospective double-blind study. The four groups were similar with regard to age, sex, duration of ulcer disease, smoking habits etc. After 2 weeks treatment 28/42 patients (66.7%) healed on famotidine 40 mg nocte, 24/42 patients (57.1%) on famotidine 20 mg bid, 26/41 patients (63.4%) on famotidine 40 mg bid and 28/43 patients (65,1%) on ranitidine 150 mg bid. The corresponding healing rates after 4 weeks were 90.5%, 83.3%, 90.2% and 93%, respectively. After 8 weeks more than 93% of the patients had healed ulcers. At each time there was no statistical difference between the different famotidine regimens and the ranitidine group. All treatments were well tolerated and severe adverse events were rare. Famotidine 40 mg at night, therefore, appears to be as good as conventional ranitidine.

Famotidine, a new H2-receptor antagonist, does not affect hepatic elimination of diazepam or tubular secretion of procainamide

In 8 healthy male volunteers the pharmacodynamic responses to a single dose of diazepam and a single dose of procainamide were assessed before and after pre-treatment with the H2-receptor antagonist famotidine in a randomized crossover study. The pharmacokinetics of diazepam and procainamide were also studied, and the binding of famotidine to human liver microsomes was also measured. Cimetidine induced binding changes with a spectral dissociation constant (Ks) of 0.87 mM, whereas famotidine produced no measurable spectral alteration in concentrations up to 4 mM. The elimination half-life (t1/2: 45.6 h) and total plasma clearance (CL: 0.28 ml/min/kg) of diazepam were not significantly altered by famotidine (t1/2 = 39.0 +/- 11.4 h; CL = 0.31 +/- 0.08 ml/min/kg). Similarly, there was no enhancement of the sedative effect of diazepam by famotidine. The pharmacodynamics and pharmacokinetics of procainamide and N-acetylprocainamide (NAPA), too, were not significantly changed by famotidine: procainamide t1/2 2.9 vs 3.0 h under famotidine and renal clearance (CLR) 436 vs 443 ml/min; and NAPA CLR 195 vs 212 ml/min under famotidine. The data suggest that famotidine, in contrast to cimetidine, does not affect the pharmacokinetics of diazepam (hepatic elimination) or procainamide (tubular secretion). This new H2-receptor antagonist appears to be devoid of an interaction potential for either type of drug elimination.

Clinical pharmacology of famotidine

The results of the initial clinical pharmacology studies of famotidine, a new H2 receptor antagonist, are summarized. These studies indicate that: single oral doses of famotidine (5-80 mg) were well tolerated; famotidine effectively suppressed basal, nocturnal, pentagastrin- and meal-stimulated acid secretion; the duration of the antisecretory action of famotidine was dose related: up to 12 h for the 20-mg dosages, and 18-24 h for the 80-mg dose; the elimination half-life was 3.8 h; 5 mg of famotidine gave acid suppression similar to that of 300 mg of cimetidine; a dose response was identified: 2 h after oral dosing, 5 mg famotidine suppressed stimulated acid secretion to 60% of control and was comparable to 300 mg cimetidine (55% suppression), whereas higher doses of famotidine yielded significantly more suppression of acid secretion (10 mg yielding 70% and 20 mg 90%), significantly greater than 300 mg cimetidine; plasma famotidine concentration and urinary recovery were dose related, and famotidine (10-40 mg) had no effect on serum prolactin. Thus, famotidine is a safe and potent H2 blocker of acid secretion with a long duration of action.

Famotidine versus ranitidine for the short-term treatment of duodenal ulcer

One-hundred and eight-three patients with endoscopically proven duodenal ulcers, enrolled in this prospective, double-blind study, were randomly allocated to receive famotidine 40 mg once at night, 20 mg twice daily, 40 mg twice daily, or ranitidine 150 mg twice daily for 2-8 weeks. Pretreatment characteristics between the four groups were similar. After 4 weeks of treatment, among the famotidine-treated patients, 38 of 42 (90.5%) healed with the 40 mg once nightly regimen, 35 of 42 (83.3%) with 20 mg twice daily, and 37 of 41 (90.2%) with 40 mg twice daily. In the ranitidine group 40 of 43 patients (93.0%) healed. After 8 weeks of treatment, the respective data were: 97.6, 95.2, 100 and 93.0%. Different results between the famotidine groups and the ranitidine group were not statistically significant. All treatments were well tolerated and severe adverse events were rare. Famotidine 40 mg given once at night appears to be as safe and effective as conventional therapy with ranitidine, indicating the importance of overnight gastric acidity in the pathogenesis of duodenal ulcer disease.

Famotidine: summary of preclinical safety assessment

Extensive preclinical safety studies with famotidine were performed or sponsored by Yamanouchi Phamaceutical Co, Ltd, Tokyo, Japan, and Merck, Sharp & Dohme Research Laboratories, West Point, Pennsylvania, USA. These studies were performed in dogs, rats, mice and rabbits, receiving oral and intravenous administration of the compound. Minimal toxicologic effects (after acute, subacute, or chronic administration) have been observed even at extremely high dosage levels (4,000 mg/kg/day) and for extended periods of administration (2,000 mg/kg/day for 105 weeks). No evidence of teratogenic, mutagenic, or carcinogenic effects or alterations of reproductive function have been seen. Based on these data, there are no contraindications for administration of this compound to humans.

Famotidine: nocturnal administration for gastric ulcer healing. Results of multicenter trials in Austria and Germany

We conducted an 8-week, double-blind, randomized, placebo-controlled multicenter trial (Austria and Germany) to determine whether famotidine would speed healing or relief of symptoms in patients with benign gastric ulcer. Of the 65 patients who completed the trial, 32 received famotidine 40 mg once at night, and 33 received placebo. At 4, 6, and 8 weeks after entry, ulcers had healed in a larger percentage of patients treated with famotidine than in those treated with placebo (German multicenter trial: 65 vs. 46%, 95 vs. 71%, and 95 vs. 79%; Austrian multicenter trial: 42 vs. 44%, 67 vs. 44%, and 92 vs. 44%). In the famotidine group, healing had occurred significantly more often after 6 weeks (p less than 0.05). Famotidine was not superior to placebo in relieving ulcer symptoms. The findings suggest that famotidine in a single evening dose significantly hastens the healing of benign gastric ulcers.

Famotidine in the management of duodenal ulcer: experience in Italy

A multicenter study that involved 15 Italian institutions was carried out to compare the efficacy and safety of famotidine 40 mg at bedtime, famotidine 20 mg b.i.d., famotidine 40 mg b.i.d., and ranitidine 150 mg b.i.d. in promoting the healing of acute duodenal ulcer. Two hundred and twenty-four patients with endoscopically proven duodenal ulcer were randomly allocated into four treatment groups. Efficacy results for the four groups were similar at weeks 2, 4, and 8 of therapy. At week 8, the percentage of patients healed in each group was as follows: 92% in the famotidine 40-mg bedtime group, 97% with 20 mg b.i.d., 93% with 40 mg b.i.d., and 90% with ranitidine 150 mg b.i.d. Day pain and night pain were markedly reduced in all four groups, antacid consumption fell considerably, and therapy was generally well tolerated. The adverse experiences evaluated by the investigator as possibly, probably, or definitely related to test medication were rare and moderate.

Famotidine (MK-208) in the treatment of gastric ulcer. Results of a multicenter double-blind controlled study

The aim of the present investigation was to study the efficacy and safety of famotidine (MK-208), a new, potent, histamine H2 receptor antagonist, in promoting the healing of active gastric ulcer when compared to placebo. Of the 71 patients who took part in this multicenter double-blind study in Italy, 37 were administered famotidine 40 mg once daily and 34 placebo. Treatment duration was for up to 8 weeks, and endoscopic and clinical studies were performed at onset and week 4 and, if necessary, at weeks 6 and 8. All patients were carefully evaluated at regular intervals for adverse drug reactions by clinical and laboratory examinations. By the end of the study, 97% of the ulcers were healed in the famotidine group compared to 66% in the placebo group (p less than 0.01). Day and night pain decreased significantly more in the famotidine group than in the placebo group. Both treatments were well tolerated, and no alterations in laboratory tests were observed. Famotidine, therefore, proved effective in the treatment of gastric ulcer and was well tolerated on a short-term basis.

Famotidine in the treatment of gastric and duodenal ulceration: overview of clinical experience

The new H2 receptor antagonist, famotidine, has been tested in open and double-blind studies in over 2,000 acute duodenal or gastric ulcer patients as well as in the maintenance of chronic duodenal ulcer patients. In early studies, dosages of 20 mg b.i.d. were found to achieve better results than 10 mg b.i.d. and equivalent to 20 mg t.i.d. Trials comparing famotidine to cimetidine, ranitidine, and gefarnate found the new agent to be approximately equivalent to cimetidine and ranitidine and superior to gefarnate in the treatment of acute duodenal ulcer. Similar trials were conducted to compare different types of therapy in acute gastric ulcer. Famotidine 40 mg at bedtime was significantly more effective than placebo, and a 20 mg b.i.d. dosage once again proved at least as active as cimetidine 200 mg q.i.d. and considerably more effective than gefarnate. Furthermore, famotidine 20 mg at bedtime was found to effectively prevent relapses for at least 6 months. The side effect profile was extremely favorable--adverse reactions were rare and never positively associated with the drug. Although experience with this new agent is still somewhat limited, preliminary results indicate that famotidine is at least comparable with the other available H2 antagonists and can be considered an excellent choice for treatment of peptic ulcer disease.

Pharmacokinetics of famotidine, a new H2-receptor antagonist, in relation to renal function

The pharmacokinetics of a new, potent H2-receptor antagonist, famotidine, 20 mg i.v. was studied in 7 subjects with normal renal function and in 24 patients with varying degrees of renal impairment. The volume of distribution at steady state was 1.141/kg in normal subjects and was not altered in renal failure. The half-life of elimination was 2.59 h in normal subjects and was unchanged in mild renal failure (creatinine clearance, CLCR 90-60 ml/min/1.48 m2) but was increased to 4.72 h in moderate renal failure (CLCR 60-30 ml/min/1.48 m2), and to 12.07 h in severe renal failure (CLCR below 30 ml/min/1.48 m2). The cumulative urinary excretion and renal clearance of famotidine were correspondingly reduced in patients with impaired kidney function. In normal subjects and in patients with mild to moderate renal failure, about 70% of famotidine was excreted through the kidney, mainly by tubular secretion. In patients with a CLCR above 60 ml/min/1.48 m2 the normal daily dose of famotidine can be employed, but in those with a CLCR between 60 and 30 ml/min/1.48 m2 the dose should be reduced by half, and in patients with a CLCR below 30 ml/min/1.48 m2 a reduction by three quarters of the normal dose is recommended.

Studies on the H2-receptor antagonism of MK-208 in isolated rabbit gastric glands

Using isolated rabbit gastric glands, the H2-receptor antagonist MK-208 was investigated with respect to its effects on [14C]aminopyrine uptake as an index of gastric acid secretion. In addition to shifting the histamine concentration-response curve to the right in a parallel fashion, the antagonism produced by MK-208 was reversible, contrary to that previously seen in the guinea pig atria. These observations suggest that the H2-receptors responsible for mediating gastric secretion in the rabbit and the chronotropic response in guinea pig atria are different.

[Human acid secretion during daily administration of H2-blockers]

The potency and duration of a single dose of ranitidine and famotidine were compared in placebo-controlled studies. In addition, the effect of a single night-time dose of famotidine (40 mg) on gastric acid secretion and basal hormone levels was assessed before, during and after a 28-day treatment. Basal acid secretion was depressed by about 73% and 76% 12 hours after 300 mg ranitidine and 40 mg famotidine respectively. Pentagastrin-stimulated acid output was reduced by about 26% and 29%. 20 hours after both drugs, basal secretion was still inhibited by about 60%, whereas no effect on stimulated acid secretion could be detected. Nocturnal gastric acidity (23.00-07.00) was inhibited from 35.8 +/- 4.6 mmol/l to 1.8 +/- 0.5 mmol/l (94% inhibition) by 40 mg bedtime famotidine , and to 1.7 +/- 0.5 mmol/l (95% inhibition) by 300 mg ranitidine. Both drugs significantly reduced H+ concentrations during the following day. On day 29, i.e. 12 hours after the last famotidine dose, basal and stimulated acid secretion was reduced by some 50% and 26% respectively. On day 35, gastric acid output had returned to pretreatment values. Basal levels of prolactin, testosterone etc. were unchanged by 28-day famotidine treatment. Rantidine and famotidine may therefore be used as a single night-time dose in the acute treatment of peptic ulcer disease.

Inhibition of gastric secretion by a new H2-antagonist, YM-11170 in healthy subjects

Oral administration of YM-11170 (5-20 mg) inhibited both basal and tetragastrin-induced gastric secretion of acid and pepsin in healthy volunteers. YM-11170 was at least 20 times more potent than cimetidine in inhibiting stimulated acid secretion. The area under the plasma concentration of YM-11170 vs time curve correlated positively to both dose and percent inhibition of acid output in response to tetragastrin. YM-11170 significantly inhibited basal and stimulated acid secretion even 10 h after a 20-mg dose. A plasma level of YM-11170 required for 50% inhibition of stimulated acid secretion was found to be 13 ng/ml. These results indicate that YM-11170 is a very potent inhibitor of gastric acid secretion and that twice daily medication of 20 mg YM-11170 is recommendable for further antisecretory studies with ulcer patients.

Method for detection of antibody against low molecular weight antigen (hapten)--production and detection of antibody against histamine H2 receptor of antibody against histamine H2 receptor antagonist "Famotidine"

Antibodies against histamine H2-receptor antagonist "Famotidine (FAMO)", molecular weight 337, chemical name; N-sulfamoyl-3-(2-guanidinothiazol-4-ylmethylthio) propionamide, were produced by subcutaneously injecting rabbits with an albumin and FAMO conjugate covalently bound with 1-ethyl-3-(3-dimethyl-amino-propyl) carbodiimide (ECDI). Two new detection systems for antibody titration were developed and employed. In one method, the antigen FAMO was tagged to sheep red blood cells (SRBC) and analysed qualitatively by a fluorescence activated cell sorter (FACS) using a second fluorescence isothiocyanate (FITC) labeled antibody. In the other method, CH-Sepharose beads were employed in place of SRBC and Horse Radish Peroxidase (HRP) was labeled to the second antibody instead of FITC used in the former method. HRP of the immune complex was colorimetrically measured with DAB-H2O2 to analyse the fine antibody titer. These high sensitive detection methods revealed the existence of IgG type of FAMO antibody. The detection sensitive detection methods revealed the existence of IgG type of FAMO antibody. The detection sensitivity was approximately 50 to 100 times higher in the later method with HRP than in the former. Furthermore these two methods could be deemed to be a good model system for a receptor assay.

Effect of H2-receptor antagonists, cimetidine and YM-11170, on serum gastrin levels in lumen-perfused rats

To determine whether cimetidine increases serum gastrin levels by elevation of intragastric pH or by other mechanisms, the effects of two different H2-receptor antagonists, cimetidine and YM-11170, on serum gastrin levels were compared in rats with controlled intragastric pH. When the intragastric pH was maintained between 4.5 and 5.5, 2-10 mumol/kg of cimetidine increased serum gastrin levels significantly, whereas no significant increase was observed after 0.02-0.1 mumol/kg of YM-11170. This occurred despite the same extent of inhibition of histamine-stimulated acid secretion as with cimetidine. When the intragastric pH was fixed at 5.5, the serum gastrin responses to cimetidine were significantly greater than to saline or YM-11170. Therefore, the increase in serum gastrin levels by cimetidine is due neither to the elevation of intragastric pH nor the result of H2-receptor blockade, but is probably due to a direct action to release gastrin.

Studies on MK-208 (YM-11170) a new, slowly dissociable H2-receptor antagonist

MK-208 [3-(((2-(aminoiminomethyl)amino)-4-thiazolyl)-methyl)thio)-N'-(a minosulfonyl) propanimidamide], also known as YM-11170, is a highly potent histamine H2-receptor antagonist in guinea-pig atria, acting via a unique binding mechanism. Unlike ranitidine, the onset of action of this compound was slow and its inhibitory action was difficult to remove from the tissues by repeated washing. Preincubation of atria with ranitidine, however, protected the H2-receptor from these prolonged inhibitory effects of MK-208. The H2-receptor antagonism produced by MK-208 was not surmountable by increasing concentrations of dimaprit. The compound did not alter the response of this tissue to isoproterenol or affect basal atrial rate under conditions where maximal H2-receptor blockade was achieved. In dogs, MK-208 was effective in inhibiting gastric acid secretion evoked by histamine, gastrin and 2-deoxy-D-glucose. Orally, it was approximately 7 times as potent as ranitidine against histamine-induced secretion, and its duration of action was substantially longer. The compound was also highly effective in inhibiting basal acid secretion in chronic gastric fistula rats.

Kinetics of antisecretory action of a new H2-antagonist, YM-11170, in conscious dogs

The antisecretory property of YM-11170 was compared with that of cimetidine and atropine in the Heidenhain pouch dog. YM-11170 inhibited competitively dimaprit-induced gastric acid secretion in doses of 33 and 100 nmol/kg per h and its antisecretory potency was 148 times more pronounced than that of cimetidine. The secretory action of pentagastrin and methacholine was also inhibited by YM-11170 and cimetidine with doses similar to those required for the inhibition of dimaprit action although the inhibition by the H2-antagonists was not of the surmountable type. Atropine inhibited gastric secretion stimulated by methacholine and pentagastrin more strongly than that stimulated by dimaprit. It is concluded that YM-11170 is a competitive antagonist of dimaprit-induced gastric secretion in vivo and that the activity of the H2-antagonists in blocking gastric H2-receptors may reflect their inhibitory effect on the acid response to pentagastrin and methacholine.

Effect of a new potent H2-receptor antagonist 3[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]-N2- sulfamoylpropionamidine (YM-11170) on gastric mucosal histamine-sensitive adenylate cyclase from guinea pig

The effect of 3[[[2-[(diaminomethylene)amino]-4- thiazolyl]methyl]thio]-N2-sulfamoylpropionamidine (YM-11170), a new thiazole H2-receptor antagonist bearing propionamidine at the terminus of a side chain, on histamine-sensitive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1] of gastric mucosa from the guinea pig was studied and compared with that of cimetidine. YM-11170 displaced the concentration-stimulation curve of histamine-sensitive adenylate cyclase to the right with a pA2 of 7.65 (Ki = 2.25 X 10(-8) M). Stimulation of gastric adenylate cyclase by 0.1 mM histamine was competitively inhibited by YM-11170 and cimetidine in a dose-dependent manner, with IC50 values of 5.9 X 10(-7) M and 1.4 X 10(-5) M respectively. Hippocampal histamine-sensitive adenylate cyclase in the presence of 0.1 mM histamine was also competitively inhibited by YM-11170 with an IC50 of 1.1 X 10(-7) M. YM-11170 did not affect Gpp(NH)p-, NaF-, PGE2-stimulated or basal activity of the gastric adenylate cyclase. These data, together with other results, indicate that YM-11170 is a highly selective and potent H2-receptor antagonist which competes with histamine at the receptor site on the histamine-sensitive adenylate cyclase.

Effect of a new potent H2-blocker, 3-]]]2-[(diaminomethylene)amino]-4-thiazolyl]methyl]-thio]-N2-sulfamoylpropionamidine (YM-11170) on gastric secretion induced by histamine and food in conscious dogs

The inhibitory effect of a new H2-receptor antagonist YM-11170 on gastric acid response to histamine and food was compared with that of cimetidine in the conscious dog with a Heidenhain pouch. When given intravenously at a steady state of gastric secretion by continuous infusion of histamine. YM-11170 was 42 times more potent and 1.3 times longer-lasting (p less than 0.05) than cimetidine in reducing the total acid output. The higher potency of YM-11170 than that of cimetidine was also demonstrated in oral antisecretory tests with histamine. The oral ED50 relative to i.v. ED50 as an indirect indication of absorption rate of the drugs was 2.9 for YM-11170 and 2.7 for cimetidine. The secretory response to food stimulation was also antagonized by oral administration of YM-11170 with 40 times greater potency than that of cimetidine. The antisecretory effects of the drugs on the histamine-induced gastric secretion were characterized by a marked decrease in the secretory volume. No behavioral change was observed in association with the H2-blockers. These results indicate that YM-11170 is a very potent inhibitor of gastric acid secretion and also suggest that the absorption rate of YM-11170 from the gastro-intestinal tract is similar to that of cimetidine.